SANGER-RIEGEL. — SULPHUR TRIOXIDE-SILICON CHLORIDE. 577 



boiling point of the mixture, hence it must he tlie former. ( 'hlor- 

 sulphonic acid, the only other compound of .sulphur which might he 

 expected, and then only in those preparations in wliich hy<lrous 

 sulphur trioxide was used, was found to be absent by a distillation with 

 salt, when only a very small amount of hydrochloric acid was given off. 

 It appears from these observations that silicon tetrachloride does 

 not behave like carbon tetrachloride with sulphur trioxide, the 

 principal reaction being represented as follows : 



2SO3 + 2SiCl4 = S2O5CI2 + SizOCle (1) 



If it did behave like carbon tetrachloride, the reaction would be: 



2SO3 + SiCl4 = S2O6CI2 + SiOCla. 



We base our contention that SiOCl2, the unknown oxychloride of 

 silicon which would be analogous to phosgene, and might therefore be 

 called silico-phosgene, is not formed on the fact that all the properties 

 of the silicon compound resulting from the reactions point to the oxy- 

 chloride, SioOCle; furthermore, on the analyses, and on our failure to 

 find the silico-phosgene in the lower boiling fraction, where it would 

 be expected. The liquid distilled from the reaction mixture below 

 130° gave on distillation sulphur trioxide vapors, a mixture of sulphur 

 trioxide and silicon-tetrachloride, an almost pure silicon tetrachloride 

 which was on several occasions re-distilled and found to boil at 56-58°, 

 its true boiling point being 57°, and a little of the higher boiling frac- 

 tion. In the distillation in vacuo, a vessel cooled with liquid air was 

 added to condense any silico-phosgene, but nothing was found there 

 beyond silicon tetrachloride and sulphur trioxide. The weights of the 

 various condensations and residues were always noted; their nature 

 being established as either unchanged substances, or as the mixture 

 of oxychloride and pyrosulphuryl chloride, nearly all the material was 

 accounted for (thus in one case 94%), so that no considerable amount 

 was left which might have formed the silico-phosgene. In nearly 

 everyone of the twenty-six preparations made the proportions taken 

 were those of two molecules of sulphur trioxide to one of silicon tetra- 

 chloride, favoring the reaction 2SO3 + SiCU = SiOCl2 + S2O6CI2; 

 nevertheless every fact points to the formation of silicon oxj-chloride, 

 and none to that of silico-phosgene. That silico-phosgene is unknown 

 also speaks against the likelihood of its formation in this reaction. 



In three cases distillates were obtained which were not very far re- 

 moved from a mixture of the two products in molecidar proportions, 

 as required by reaction (1), but in most cases there was a decided excess 



